Claims:

1. A cross-linkable nitrile rubber composition containing a highly
saturated nitrile rubber (a) having an α,β-ethylenically
unsaturated nitrile monomer unit and a carboxyl-group containing monomer
unit and having an iodine value of 120 or less, a cross-linking agent
(b), and a cyclic amidine and/or cyclic amidinium salt (c) of the
following formula (1): ##STR00003## (wherein, R1 and R2
independently indicate a hydrogen atom, an alkoxy group, an alkyl group
which may have a substituent, alkenyl group which may have a substituent,
or aryl group which may have a substituent, R1 and R2 may bond
to form a cyclic structure, and, further, R3 indicates an alkylene
group or alkenylene group which may have a substituent.)

2. The cross-linkable nitrile rubber composition as set forth in claim 1,
wherein said cross-linking agent (b) is a polyamine-based cross-linking
agent (d).

5. The cross-linkable nitrile rubber composition as set forth in claim 1,
wherein said cyclic amidine and/or cyclic amidinium salt (c) is
1,8-diazabicyclo[5,4,0]undecene-7 or its salt.

6. The cross-linkable nitrile rubber composition as set forth in claim 1,
wherein a ratio of content of said cross-linking agent (b) is 0.1 to 20
parts by weight with respect to 100 parts by weight of said highly
saturated nitrile rubber (a).

7. The cross-linkable nitrile rubber composition as set forth in claim 1,
wherein a ratio of content of said cyclic amidine and/or cyclic amidinium
salt (c) is 0.1 to 20 parts by weight with respect to 100 parts by weight
of said highly saturated nitrile rubber (a).

9. A cross-linked rubber obtained by cross-linking the cross-linkable
nitrile rubber composition as set forth in claim 1.

10. The cross-linked rubber as set forth in claim 9, which is a belt or
seal material.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a cross-linkable nitrile rubber
composition giving cross-linked rubber with a small compression set and
an excellent heat resistance.

BACKGROUND ART

[0002]In the past, as rubber with an excellent oil resistance, heat
resistance, and ozone resistance, a nitrile-group containing highly
saturated copolymer rubber (also called "highly saturated nitrile
rubber", hydrogenated nitrile rubber included) has been known. Its
cross-linked rubber is being used as materials for belts, hoses, gaskets,
packings, oil seals, and various other automotive use rubber products.
However, due to the increasingly smaller size and higher output of
automobile engines, rubber materials more superior in heat resistance
have become sought. Further, when using highly saturated nitrile rubber
for seal applications, further reduction in compression set becomes
necessary.

[0003]In the face of these circumstances, Patent Document 1 proposes a
cross-linkable rubber composition containing highly saturated nitrile
rubber having α,β-ethylenically unsaturated dicarboxylic acid
monoester monomer units, a polyamine-based cross-linking agent and basic
cross-linking accelerator. While this composition gives cross-linked
rubber improved in heat resistance and compression set to a certain
extent, further improvement of the compression set while maintaining the
heat resistance in a good state has been sought.

[0005]An object of the present invention is to provide a cross-linkable
nitrile rubber composition giving a cross-linked rubber with a good heat
resistance (heat aging resistance) and an excellent compression set and
cross-linked rubber of the same.

Means for Solving the Problems

[0006]The inventors engaged in intensive research to solve the above
problem and as a result discovered that by blending into a specific
highly saturated nitrile rubber a cross-linking agent and a specific
amidine or amidinium salt and cross-linking the mixture, the above object
can be achieved and thereby completed the present invention.

[0007]Therefore, according to the present invention, there are provided:

(1) A cross-linkable nitrile rubber composition containing a highly
saturated nitrile rubber (a) having an α,β-ethylenically
unsaturated nitrile monomer unit and a carboxyl-group containing monomer
unit and having an iodine value of 120 or less, a cross-linking agent
(b), and a cyclic amidine and/or cyclic amidinium salt (c) of the
following formula (1):

##STR00001##

[0008](wherein, R1 and R2 independently indicate a hydrogen
atom, an alkoxy group, an alkyl group which may have a substituent,
alkenyl group which may have a substituent, or aryl group which may have
a substituent, R1 and R2 may bond to form a cyclic structure,
and, further, R3 indicates an alkylene group or alkenylene group
which may have a substituent.);

(2) The cross-linkable nitrile rubber composition as set forth above
wherein the above cross-linking agent (b) is a polyamine-based
cross-linking agent (d);(3) The cross-linkable nitrile rubber composition
as set forth above wherein the above carboxyl-group containing monomer
unit is an α,β-ethylenically unsaturated dicarboxylic acid
monoester monomer unit;(4) The cross-linkable nitrile rubber composition
as set forth above wherein the above cyclic amidine and/or cyclic
amidinium salt (c) has a polycyclic structure;(5) The cross-linkable
nitrile rubber composition as set forth above wherein the above cyclic
amidine and/or cyclic amidinium salt (c) is
1,8-diazabicyclo[5,4,0]undecene-7 or its salt;(6) The cross-linkable
nitrile rubber composition as set forth above wherein a ratio of content
of the above cross-linking agent (b) is 0.1 to 20 parts by weight with
respect to 100 parts by weight of the above highly saturated nitrile
rubber (a);(7) The cross-linkable nitrile rubber composition as set forth
above wherein a ratio of content of the above cyclic amidine and/or
cyclic amidinium salt (c) is 0.1 to 20 parts by weight with respect to
100 parts by weight of the above highly saturated nitrile rubber (a);(8)
The cross-linkable nitrile rubber composition as set forth above further
containing carbon black and/or silica;(9) A cross-linked rubber obtained
by cross-linking the cross-linkable nitrile rubber composition as set
forth above; and(10) The cross-linked rubber as set forth above which is
a belt or seal material.

EFFECTS OF THE INVENTION

[0009]According to the present invention, there is provided a
cross-linkable nitrile rubber composition giving a cross-linked rubber
with a good heat resistance (heat aging resistance) and an excellent
compression set.

BEST MODE FOR CARRYING OUT THE INVENTION

Cross-Linkable Nitrile Rubber Composition

[0010]The cross-linkable nitrile rubber composition of the present
invention is one containing a highly saturated nitrile rubber (a) having
an α,β-ethylenically unsaturated nitrile monomer unit and a
carboxyl-group containing monomer unit and having an iodine value of 120
or less, a cross-linking agent (b), and a cyclic amidine and/or cyclic
amidinium salt (c) expressed by the formula (1).

[0011]Highly Saturated Nitrile Rubber (a)

[0012]The monomer forming the α,β-ethylenically unsaturated
nitrile monomer unit of the highly saturated nitrile rubber (a) (below,
sometimes referred to as an "α,β-ethylenically unsaturated
nitrile") is not limited so long as an α,β-ethylenically
unsaturated compound having a nitrile group. An acrylonitrile;
α-chloroacrylonitrile, α-bromoacrylonitrile, or other
α-halogenoacrylonitriles; a methacrylonitrile, or other
α-alkyl acrylonitriles etc. may be mentioned. An acrylonitrile and
methacrylonitrile are preferable. The α,β-ethylenically
unsaturated nitrile may be used in combination.

[0013]The content of the α,β-ethylenically unsaturated nitrile
monomer unit in the highly saturated nitrile rubber (a) is preferably 10
to 60 wt %, more preferably 15 to 55 wt %, particularly preferably 20 to
50 wt %. If the content of the α,β-ethylenically unsaturated
nitrile monomer unit is too small, the cross-linked rubber is liable to
drop in oil resistance, while conversely if too large, the cold
resistance may drop.

[0014]The carboxyl-group containing monomer unit of the highly saturated
nitrile rubber (a) is a unit of a monomer having at least one free
carboxyl group (carboxyl group not substituted by a metal salt etc.) or
its anhydride bond. By including such a carboxyl-group containing monomer
unit, the obtained cross-linked rubber can be made one with excellent
tensile stress.

[0015]As the monomer forming the carboxyl-group containing monomer unit,
an α,β-ethylenically unsaturated monocarboxylic acid,
α,β-ethylenically unsaturated dicarboxylic acid monoester,
α,β-ethylenically unsaturated polyvalent carboxylic acid, or
an anhydride of the same is preferable. Since the effect of the present
invention becomes much more remarkable, an α,β-ethylenically
unsaturated dicarboxylic acid monoester is particularly preferable.

[0016]As the organic group bonding with the carbonyl group through an
oxygen atom at the ester part of the α,β-ethylenically
unsaturated dicarboxylic acid monoester, an alkyl group, cycloalkyl
group, or alkyl cycloalkyl group is preferable, while an alkyl group is
particularly preferable. The alkyl group preferably has 1 to 10 carbon
atoms, more preferably 2 to 6 carbon atoms, the cycloalkyl group
preferably has 5 to 12 carbon atoms, more preferably 6 to 10 carbon
atoms, and the alkyl cycloalkyl group preferably has 6 to 12 carbon
atoms, more preferably 7 to 10 carbon atoms. If the number of carbon
atoms of the organic group is too small, the cross-linkable nitrile
rubber composition is liable to drop in working stability, while
conversely if the number of carbon atoms is too large, the cross-linking
speed may become lower or the cross-linked rubber may drop in mechanical
properties.

[0018]Among these as well, from the viewpoint of the effect of the present
invention appearing much more remarkably, monopropyl maleate,
mono-n-butyl maleate, monopropyl fumarate, mono-n-butyl fumarate,
monopropyl citraconate, mono-n-butyl citraconate, and other monoesters of
dicarboxylic acids having carboxyl groups at the two carbon atoms forming
the α,β-ethylenically unsaturated bond are preferable,
mono-n-butyl maleate, monopropyl citraconate, and other monoesters of
dicarboxylic acids having two carboxyl groups at the cis positions (cis
arrangement) are more preferable, and mono-n-butyl maleate is
particularly preferable.

[0022]The content of the carboxyl-group containing monomer unit in the
highly saturated nitrile rubber (a) is preferably 0.1 to 20 wt %, more
preferably 0.2 to 15 wt %, particularly preferably 0.5 to 10 wt %. If the
content of the monomer unit having a carboxyl group is too small, the
tensile stress of the cross-linked rubber is liable to fall, while
conversely if too large, the cross-linkable nitrile rubber composition
may deteriorate in scorch stability or the cross-linked rubber may drop
in fatigue resistance.

[0024]As examples of the diene monomer forming the diene monomer unit,
1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and
other C4 or higher conjugated diene monomers; 1,4-pentadiene,
1,4-hexadiene, and other preferably C5 to C12 nonconjugated
diene monomers; may be mentioned. Among these, a conjugated diene monomer
is preferable, and 1,3-butadiene is more preferable.

[0026]The content of the diene monomer unit and/or α-olefin monomer
unit in the highly saturated nitrile rubber (a) is preferably 20 to 89.9
wt %, more preferably 30 to 84.8 wt %, particularly preferably 40 to 79.5
wt %. If the content is too small, the cross-linked rubber is liable to
drop in rubber elasticity, while conversely if too large, the heat
resistance and the chemical resistance stability may be impaired.

[0027]The highly saturated nitrile rubber (a) can further contain a unit
of other monomer able to copolymerize with the
α,β-ethylenically unsaturated nitrile monomer, carboxyl-group
containing monomer, and diene monomer and/or α-olefin monomer. As
such other monomer, an α,β-ethylenically unsaturated
carboxylic acid ester monomer other than an α,β-ethylenically
unsaturated dicarboxylic acid monoester monomer, an aromatic vinyl
monomer, a fluorine-containing vinyl monomer, a copolymerizable antiaging
agent, etc. may be mentioned.

[0033]These other copolymerizable monomers may also be used in
combination. The content of the other monomer units of the highly
saturated nitrile rubber (a) is preferably 50 wt % or less, more
preferably 40 wt % or less, particularly preferably 10 wt % or less.

[0034]The content of the carboxyl groups in the highly saturated nitrile
rubber (a) used in the present invention, that is, the number of moles of
the carboxyl group per 100 g of the highly saturated nitrile rubber (a),
is preferably 5×10-4 to 5×10-1 ephr, more
preferably 1×10-3 to 1×10-1 ephr, particularly
preferably 5×10-3 to 6×10-2 ephr. If the content of
the carboxyl group of the highly saturated nitrile rubber (a) is too
small, the cross-linkable nitrile rubber composition will not
sufficiently cross-link and the cross-linked rubber is liable to fall in
tensile stress, while conversely if too large, the cross-linkable nitrile
rubber composition may deteriorate in scorch stability or the
cross-linked rubber may fall in fatigue resistance.

[0035]The highly saturated nitrile rubber (a) is one with an iodine value
of 120 or less, preferably 80 or less, more preferably 25 or less,
particularly preferably 15 or less. If the highly saturated nitrile
rubber (a) is too high in iodine value, the cross-linked rubber is liable
to fall in ozone resistance.

[0036]Further, the highly saturated nitrile rubber (a) has a polymer
Mooney viscosity (ML1+4, 100° C.) of preferably 15 to 200,
more preferably 20 to 150, particularly preferably 30 to 120. If the
highly saturated nitrile rubber (a) is too low in Mooney viscosity, the
cross-linked rubber is liable to drop in strength characteristics, while
conversely if too high, the cross-linkable nitrile rubber composition may
drop in workability.

[0037]The method of production of the highly saturated nitrile rubber (a)
is not particularly limited. In general, the method of copolymerization
of an α,β-ethylenically unsaturated nitrile monomer, a
carboxyl-group containing monomer, a diene monomer, and/or an
α-olefin monomer, and other copolymerizable monomers added in
accordance with need is convenient and preferable. As the polymerization
method, any of the known emulsion polymerization method, suspension
polymerization method, bulk polymerization method, and solution
polymerization method may be used, but due to the ease of control of the
polymerization reaction, the emulsion polymerization method is
preferable.

[0038]If the copolymer obtained by copolymerization has an iodine value
higher than 120, the copolymer may be hydrogenated. The method of
hydrogenation is not particularly limited. A known method may be
employed.

[0039]Further, to introduce a carboxyl-group containing monomer unit in
the highly saturated nitrile rubber (a), it is also possible to employ
the method of production of polymerization of the highly saturated
nitrile rubber, then addition of a compound having an alkoxycarbonyl
group, carboxyl group, or acid anhydride group to the polymer and
hydrolyzing the result in accordance with need. As the compound having
the alkoxycarbonyl group, carboxyl group, or acid anhydride group in this
case, an α,β-ethylenically unsaturated monocarboxylic acid,
α,β-ethylenically unsaturated polyvalent carboxylic acid, or
their anhydrides, an α,β-ethylenically unsaturated carboxylic
acid ester other than the above α,β-ethylenically unsaturated
dicarboxylic acid monoester monomer, etc. may be mentioned.

[0042]The cross-linking agent (b) is not particularly limited so long as
able to cross-link the highly saturated nitrile rubber (a). A
sulfur-based cross-linking agent, organic peroxide, polyamine-based
cross-linking agent (d), etc. may be mentioned, but since the effect of
the present invention becomes much more remarkable, a polyamine-based
cross-linking agent (d) is preferable.

[0045]The polyamine-based cross-linking agent (d) is not particularly
limited so long as a compound having two or more amino groups or one
becoming a compound having two or more amino groups at the time of
cross-linking, but an aliphatic hydrocarbon or an aromatic hydrocarbon
with a plurality of hydrogen atoms substituted by an amino group or
hydrazide structure (structure expressed by --CONHNH2, where CO
indicates a carbonyl group) is preferable. As specific examples,
hexamethylene diamine, hexamethylene diamine carbamate, tetramethylene
pentamine, hexamethylene diamine cinnamaldehyde adduct, hexamethylene
diamine dibenzoates, and other aliphatic polyvalent amines;
2,2-bis{4-(4-aminophenoxy)phenyl}propane, 4,4'-methylene dianiline,
m-phenylene diamine, p-phenylene diamine, 4,4'-methylene
bis(o-chloroaniline), and other aromatic polyvalent amines; dihydrazide
isophthalate, dihydrazide adipate, dihydrazide sebacate, and other
compounds having two or more hydrazide structures; etc. may be mentioned,
but hexamethylene diamine carbamate is particularly preferable.

[0046]The content of the cross-linking agent (b) in the cross-linkable
nitrile rubber composition of the present invention is, with respect to
the highly saturated nitrile rubber (a) as 100 parts by weight,
preferably 0.1 to 20 parts by weight, more preferably 0.2 to 15 parts by
weight, particularly preferably 0.5 to 10 parts by weight. If the content
of the cross-linking agent (b) is too small, a cross-linked rubber with
excellent heat resistance and small compression set is liable not to be
obtainable, while if too large, the cross-linked rubber may fall in
fatigue resistance.

[0049](wherein, R1 and R2 independently indicate a hydrogen
atom, an alkoxy group, an alkyl group which may have a substituent,
alkenyl group which may have a substituent, or aryl group which may have
a substituent, R1 and R2 may bond to form a cyclic structure,
and, further, R3 indicates an alkylene group or alkenylene group
which may have a substituent.)

[0050]As the alkoxy group, a methoxy group, ethoxy group, or other C1
to C5 alkoxy group may be mentioned.

[0051]In the alkyl group which may have a substituent, as the substituent,
a halogen atom, hydroxy group, carboxyl group, alkoxy group, carbonyl
group, amino group, alkoxycarbonyloxy group, nitro group, or aryl group
may be mentioned. Further, the alkyl group preferably has 1 to 5 carbon
atoms.

[0052]In the alkenyl group which may have a substituent, as the
substituent, a halogen atom, hydroxy group, alkoxy group, carbonyl group,
amino group, alkoxycarbonyloxy group, nitro group, or aryl group may be
mentioned. Further, the alkenyl group preferably has 1 to 5 carbon atoms.

[0053]In the aryl group which may have a substituent, as the substituent,
a halogen atom, hydroxy group, alkoxy group, carbonyl group, amino group,
alkoxycarbonyloxy group, nitro group, or aryl group may be mentioned.
Further, the aryl group preferably has 6 to 12 carbon atoms.

[0054]Further, since the effect of the present invention becomes much more
remarkable, R1 and R2 bonding to form a cyclic structure (that
is, the "cyclic amidine and/or cyclic amidinium ion salt (c)" having a
polycyclic structure) is preferable. Further, when the R1 and
R2 bond to form a cyclic structure, the cyclic structure may also
have a carbon-carbon unsaturated bond. Further, part of the carbon
framework forming the cyclic structure may be substituted by a nitrogen
atom, but R1 and R2 bonding and their bonding to form a C3
to C8 alkylene group which may have a substituent is preferable.
Note that the alkylene group in the alkylene group which may have a
substituent has 3 to 8 carbon atoms, preferably 3 to 5, particularly
preferably 5. Further, as the substituent, a substituent similar to the
above-mentioned alkyl group which may have a substituent may be
mentioned. Note that since the effect of the present invention becomes
much more remarkable, the alkylene group which the R1 and R2
bond to form is more preferably an unsubstituted polymethylene group.

[0055]Furthermore, as R3, a C3 to C8 alkylene group or
C3 to C8 alkenylene group which may have a substituent is
preferable, a C3 to C5 alkylene group which may have a
substituent is more preferable, and a C3 alkylene group which may
have a substituent is particularly preferable. As the substituent in the
alkylene group or alkenylene group which may have a substituent, an alkyl
group, halogen atom, hydroxy group, alkoxy group, carbonyl group, amino
group, alkoxycarbonyloxy group, nitro group, or aryl group may be
mentioned. Further, the alkylene group or alkenylene group of R3 may
also have a structure condensed with the benzene ring etc. However, as
R3, since the effect of the present invention becomes much more
remarkable, a C3 to C8 nonsubstituted polymethylene group is
preferable, a C3 to C5 nonsubstituted polymethylene group is
more preferable, and a C3 nonsubstituted polymethylene group is
particularly preferable.

[0056]As the cyclic amidine compound shown by the above general formula
(1), a compound having an imidazole ring, a compound having an
imidazoline ring, a compound having a tetrahydropyrimidine ring, and a
compound where R1 and R2 bond to form a cyclic structure (one
having a polycyclic structure) are preferable, while a compound where
R1 and R2 bond to form a cyclic structure is particularly
preferable since the effect of the present invention becomes much more
remarkable.

[0059]As a compound having a tetrahydropyrimidine ring,
1-methyl-1,4,5,6-tetrahydropyrimidine,
1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, etc. may be mentioned.

[0060]The compound where R1 and R2 bond to form a cyclic
structure is not particularly limited, but
1,8-diazabicyclo[5,4,0]undecene-7 (hereinafter sometimes abbreviated as
"DBU") and 1,5-diazabicyclo[4,3,0]nonene-5 (hereinafter sometimes
abbreviated as "DBN") are preferable, while
1,8-diazabicyclo[5,4,0]undecene-7 is particularly preferable.

[0061]The cyclic amidinium salt (c) used in the present invention is a
salt of cyclic amidine (c) expressed by the formula (1). As the compound
forming the salt, an organic carboxylic acid and alkyl phosphoric acid
(including a zinc dialkyl diphosphate) is preferable, and an organic
carboxylic acid is particularly preferable. As the organic carboxylic
acid, saturated monocarboxylic acid, saturated polyvalent carboxylic
acid, unsaturated monocarboxylic acid, unsaturated polyvalent carboxylic
acid, a carboxylic acid having a cyclic structure, etc. may be mentioned.
Note that the cyclic amidinium salt (c) can be obtained by using the
cyclic amidine (c) expressed by the formula (1) and reacting the compound
forming a salt in an amount of 0.5 to 2 moles with respect to 1 mole of
the cyclic amidine (c) expressed by the formula (1).

[0067]Among these, a saturated monocarboxylic acid and saturated
polyvalent carboxylic acid is preferable, a saturated monocarboxylic acid
is more preferable, and formic acid is particularly preferable.

[0068]The cyclic amidine and/or cyclic amidinium ion salt (c) expressed by
the formula (1) may be used formed into tablets by clay, talc,
diatomaceous earth, etc. for the purpose of improving the precision of
compounding and the handling when in a liquid state.

[0069]The lower limit of the total amount of the cyclic amidine and cyclic
amidinium ion salt (c) expressed by the formula (1) with respect to the
highly saturated nitrile rubber (a) as 100 parts by weight is preferably
0.1 part by weight, more preferably 0.3 part by weight, particularly
preferably 0.5 part by weight, while the upper limit is preferably 20
parts by weight, more preferably 10 parts by weight, particularly
preferably 5 parts by weight.

[0070]If the amount of the cyclic amidine and/or cyclic amidinium ion salt
(c) expressed by the formula (1) is too small, the cross-linking speed
becomes too slow and the cross-linking density falls in some cases, while
if the amount is too great, the cross-linking speed becomes too fast and
scorching occurs or the storage stability is impaired in some cases.

[0071]The cross-linkable nitrile rubber composition of the present
invention preferably contains a reinforcing filler of carbon black and/or
silica. The lower limit of the total amount of carbon black and silica
with respect to the highly saturated nitrile rubber (a) as 100 parts by
weight is preferably 0.1 part by weight, more preferably 0.5 part by
weight, still more preferably 1 part by weight, particularly preferably
10 parts by weight, while the upper limit is preferably 300 parts by
weight, more preferably 200 parts by weight, particularly preferably 120
parts by weight. If the total amount of the carbon black and silica is
too small, the rubber sometimes falls in strength, while if the total
amount is too large, the viscosity rises and the moldability is impaired
in some cases.

[0072]The carbon black is not particularly limited, but is suitably one
usually used for rubber formulations. For example, furnace black,
acetylene black, thermal black, channel black, graphite, etc. may be
used, but furnace black is preferable since the effect of the present
invention becomes much more remarkable.

[0074]Further, the particle size of the carbon black is preferably 15 to
200 nm, more preferably 18 to 100 nm, the nitrogen adsorption specific
surface area is preferably 10 to 260 m2/g, more preferably 20 to 240
m2/g, and the DBP oil absorption is preferably 50 to 200 ml/100 g,
more preferably 70 to 180 ml/100 g.

[0075]The silica is not particularly limited, but when expressed by a
formula, a compound including (SiO2) in the formula is preferable.
Specifically, quartz powder, silica powder, and other natural silica;
anhydrous silicic acid (silica gel, aerogel, etc.), hydrous silicic acid,
and other synthetic silica; silicic acid metal salt etc. may be
mentioned. Among these, synthetic silica or a silicic acid metal salt is
preferable.

[0076]Note that the natural silica and synthetic silica is one having the
formula expressed by (SiO2) or (SiO.nH2O). As the synthetic
silica, use of anhydrous synthetic silica is preferable. The anhydrous
synthetic silica is preferably one generally used as a filler of
synthetic rubber called a "white filler" (white carbon).

[0078]Further, the cross-linkable nitrile rubber composition of the
present invention may have blended into it rubber other than the highly
saturated nitrile rubber (a) in a range not impairing the effects of the
present invention. When blending in a rubber other than the highly
saturated nitrile rubber (a), 30 parts by weight or less with respect to
the highly saturated nitrile rubber (a) as 100 parts by weight is
preferable, 20 parts by weight or less is more preferable, and 10 parts
by weight or less is particularly preferable.

[0079]The cross-linkable nitrile rubber composition of the present
invention is prepared by mixing the above ingredients in preferably a
non-aqueous system. The method of preparing the cross-linkable nitrile
rubber composition of the present invention is not limited, but usually
the ingredients other than the cross-linking agent (b) and the cyclic
amidine and/or cyclic amidinium salt (c) expressed by the above formula
(1) and compounding agents unstable with respect to heat are kneaded by a
Bambury mixer, intermixer, kneader, or other mixer on a primary basis,
then are transferred to a roll etc. where the cross-linking agent (b),
the cyclic amidine and/or cyclic amidinium salt (c) expressed by the
above formula (1), etc. are kneaded on a secondary basis.

[0081]The cross-linkable nitrile rubber composition of the present
invention has a Mooney viscosity (MI1+4, 100° C.) (compound
Mooney) of preferably 15 to 150, more preferably 50 to 120. The
cross-linkable nitrile rubber composition of the present invention is
superior in moldability by having the above compound Mooney.

[0082]Cross-Linked Rubber

[0083]The cross-linked rubber of the present invention is obtained by
cross-linking the cross-linkable nitrile rubber composition.

[0084]To cross-link the cross-linkable nitrile rubber composition of the
present invention to obtain cross-linked rubber, the composition is
molded by a molding machine appropriate for the desired shaped such as an
extruder, injection molding machine, press, rolls, etc. and fixed in
shape as a cross-linked product by a cross-linking reaction. It may be
molded in advance, then cross-linked or, molded and cross-linked
simultaneously. The molding temperature is, usually, 10 to 200°
C., preferably 25 to 120° C. The cross-linking temperature is,
usually, 100 to 200° C., preferably 130 to 190° C., while
the cross-linking time is, usually, 1 minute to 24 hours, preferably 2
minutes to 1 hour.

[0085]Further, depending on the shape, size, etc. of the cross-linked
rubber, sometimes even if the surface is cross-linked, the inside may not
be sufficiently cross-linked, so further heating may be applied for
secondary cross-linking.

[0087]Below, production examples, invention examples, and comparative
examples will be given to explain the present invention in more detail.
However, the present invention is not limited to these examples. In the
following formulations, the "parts" and "%" are based on weight unless
otherwise specially indicated. The tests and evaluations were performed
as follows.

(1) Carboxyl Group Content

[0088]The content of carboxyl group in the rubber was found using a 0.02N
hydrous ethanol solution of potassium hydroxide by titration at room
temperature using thymol phthalein as an indicator as the number of moles
of the carboxyl group with respect to 100 g of the rubber. The unit was
ephr.

[0090]A cross-linkable nitrile rubber composition was placed in a length
15 cm, width 15 cm, depth 0.2 cm mold and press formed, while pressing by
a press pressure of 10 MPa, at 170° C. for 20 minutes to obtain a
sheet-shaped cross-linked product. This was transferred to a gear type
oven where it was secondarily cross-linked at 170° C. for 4 hours.
The obtained sheet-shaped cross-linked product was punched by a No. 3
dumbbell cutter to prepare a test piece. This test piece was used in
accordance with JIS K6251 for measurement of the tensile strength,
hardness, and elongation of the cross-linked rubber.

(4) O-Ring Compression Set

[0091]An inside diameter 30 mm, ring diameter 3 mm mold was used to
cross-link a cross-linkable nitrile rubber composition at 170° C.
for 20 minutes by press pressure of 10 MPa, then secondary cross-linking
was performed at 170° C. for 4 hours to obtain an O-ring test
piece. The compression set was measured using this O-ring test piece held
in a 25% compressed state at 150° C. for 500 hours in accordance
with JIS K6262.

(5) Heat Aging Test (Elongation and Change Rate in Elongation)

[0092]Test pieces prepared by primary and secondary cross-linking in the
same way as the above (3) were measured in accordance with JIS K6257
(Normal Oven Method) for elongation after 500 hours at 150° C. The
change rate of the elongation due to the heat aging was found.

Production Example 1

[0093]A metal bottle was charged with ion exchanged water in 180 parts,
concentration 10 wt % of sodium dodecyl benzenesulfonate aqueous solution
in 25 parts, acrylonitrile in 37 parts, mono-n-butyl maleate in 6 parts,
and t-dodecylmercaptan (molecular weight adjuster) in 0.75 part in that
order, the inside gas was replaced with nitrogen three times, then
1,3-butadiene in 57 parts was charged. The metal bottle was held at
5° C., cumen hydroperoxide (polymerization initiator) in 0.1 part
was charged, then a polymerization reaction caused for 16 hours while
rotating the metal bottle. A concentration 10 wt % of hydroquinone
(polymerization anticatalyst) aqueous solution in 0.1 part was added to
stop the polymerization reaction, then a water temperature 60° C.
rotary evaporator was used to remove the residual monomer to obtain a
latex of an acrylonitrile-butadiene-mono-n-butyl maleate copolymer rubber
of acrylonitrile units 34 wt %, butadiene units 60 wt %, and mono-n-butyl
maleate units 6 wt % (value measured by 1H-NMR analysis) (solids
concentration of about 30 wt %).

[0094]Further, the latex obtained above was placed in an autoclave, then
the autoclave was charged with a palladium catalyst (mixed solution of 1
wt % palladium acetate acetone solution and equal amount by weight of ion
exchanged water) to give a content of palladium with respect to the
weight of the rubber contained in the latex of 1000 ppm, and the mixture
was hydrogenated at a hydrogen pressure of 3 MPa and a temperature of
50° C. for 6 hours to obtain a nitrile-group containing highly
saturated copolymer rubber latex. To the obtained nitrile-group
containing highly saturated copolymer rubber latex, a two-fold volume of
methanol was added to coagulate the nitrile-group containing highly
saturated copolymer rubber, then this was vacuum dried at 60° C.
for 12 hours to obtain a highly saturated nitrile rubber (a1). The highly
saturated nitrile rubber (a1) had an iodine value of 10, a carboxyl group
content of 3.2×10-2 ephr, and a polymer Mooney viscosity
(ML1+4, 100° C.) of 45. Further, according to 1H-NMR
analysis, the composition of the highly saturated nitrile rubber (a1) was
acrylonitrile units 34 wt %, butadiene units 60 wt % (including
hydrogenated parts), and mono-n-butyl maleate units 6 wt %.

Example 1

[0095]A Bambury mixer was used to add and mix, into a highly saturated
nitrile rubber (a1) of 100 parts, FEF carbon black (product name "Seast
SO", made by Tokai Carbon) in 40 parts, a trimellitic acid ester (product
name "ADK Cizer C-8", made by ADEKA, plasticizer) in 5 parts, stearic
acid (cross-linking accelerator activator) in 1 part, a mixed phosphorus
acid ester (product name "Phosphanol RL210", made by Toho Chemical
Industry, working aid) in 1 part,
4,4'-di-(α,α'-dimethylbenzyl)diphenylamine (product name
"Naugard 445", made by Crompton, antiaging agent) in 1.5 parts, and
2-mercaptobenzimidazole (product name "Nocrac MB", made by Ouchi Shinko
Chemical Industry, antiaging agent) in 1.5 parts, then the mixture was
transferred to a roll and kneaded with VUCOFAC ACT 55 [made by
SAFIC-ALCAN UK: 1,8-diazabicyclo[5,4,0]undecene-7 (DBU) 70% (including
part of DBU forming formate), amorphous silica 30%] in 2 parts, and
hexamethylene diamine carbamate (product name "Diak#1", made by Dupont
Dow Elastomer, polyamine-based cross-linking agent) in 2.6 parts to
prepare a cross-linkable nitrile rubber composition.

[0097]Except for changing the 2 parts of VUCOFAC ACT 55 (made by
SAFIC-ALCAN UK) to 4 parts of RHENOGRAN XLA-60 (GE2014) [made by
RheinChemie: DBU 60% (including part of DBU forming zinc dialkyl
diphosphate salt), acrylic acid polymer and dispersant 40%], the same
procedure was performed as in Example 1 to prepare a cross-linkable
nitrile rubber composition. The obtained cross-linkable nitrile rubber
composition was used to test and evaluate the compound Mooney viscosity,
normal physical properties, heat aging resistance, and O-ring compression
set. The results are shown in Table 1.

Example 3

[0098]Except for changing the 2 parts of VUCOFAC ACT 55 (made by
SAFIC-ALCAN UK) to 1 part of ALCANPOUDRE DBU 70-3KG (GE-2014) (made by
SAFIC-ALCAN UK: DBU 70%, filler 30%), the same procedure was performed as
in Example 1 to prepare a cross-linkable nitrile rubber composition. The
obtained cross-linkable nitrile rubber composition was used to test and
evaluate the compound Mooney viscosity, normal physical properties, heat
aging resistance, and O-ring compression set. The results are shown in
Table 1.

Comparative Example 1

[0099]Except for changing the 2 parts of VUCOFAC ACT 55 (made by
SAFIC-ALCAN UK) to 2 parts of 1,3-di-o-tolyl guanidine (product name
"Noccelar DT", made by Ouchi Shinko Chemical Industry, cross-linking
accelerator), the same procedure was performed as in Example 1 to prepare
a cross-linkable nitrile rubber composition. The obtained cross-linkable
nitrile rubber composition was tested and evaluated in the same way as in
Example 1. The results are shown in Table 1.

Comparative Example 2

[0100]Except for changing the 2 parts of VUCOFAC ACT 55 (made by
SAFIC-ALCAN UK) to 2 parts of 1,3-diphenyl guanidine (product name
"Noccelar D", made by Ouchi Shinko Chemical Industry, cross-linking
accelerator), the same procedure was performed as in Example 1 to prepare
a cross-linkable nitrile rubber composition. The obtained cross-linkable
nitrile rubber composition was tested and evaluated in the same way as in
Example 1. The results are shown in Table 1.

[0101]As shown in Table 1, the cross-linkable nitrile rubber compositions
of the invention examples were good in heat resistance (heat aging test)
and small in compression set, these were excellent. As opposed to this,
in Comparative Examples 1 and 2 which did not contain the cyclic amidine
and/or cyclic amidinium salt (c) expressed in the above formula (1) and
therefore did not satisfy the requirements of the present invention, the
heat resistance (heat aging test) was good, but the O-ring compression
set was inferior.